Gland

Exocrine glands: classification by secretion modes

A. Holocrine = entire cells (easily see cells undergoing proliferation at the basal) B. Merocrine = dissolved materials (only granules are exocytosed via docking, fusing, release; cells intact) C. Apocrine = pieces/chunks of cells (parts of the cells are released together with secretory granules)

Classification of Exocrine Glands

Number of cells 1. Unicellular: goblet cells, in lining of intestine and upper respiratory tract 2. Multicellular: several types characterized by arrangement of glandular cells and organization of ducts

Major salivary glands

Parotid (contains lots of mitochondria for use of energy) + Submandibular + Sublingual gland Contain serous and mucous cells

Classification of Exocrine glands by Secretion Modes

1. Merocrine: exocytosis (release of substances produced by the secretory cells) without loss of cytoplasm (cell remains intact) -most common form of secretion -vesicles inside the cell (when receiving the signal to release) will move to the top of the cells (DOCKING) and attach to membrane (PRIMING) and then fuse (FUSION) with the cytoplasm to be released into the lumen space of the gland; cell remains intact. Ex. salivary gland acinar cell Note: sweat glands -Sweat glands have a type of secretion of merocrine, but it's specifically known as eccrine = secretion by sweat glands; produce a clear, odorless substance, consisting primarily of water and NaCl (bacteria on our skin causes the odor) 2. Holocrine: whole cell is discharged Ex. Sebaceous gland in the mucosa of cheek: -has a very short duct and is a simple branched acinar (only one short duct); shape of the secretory portion is like a flask (pear-shaped saccules); discharge sebum. 3. Apocrine: secretory product and portion of the cytoplasm are released. Ex. Mammary gland and specialized sweat glands.

Secretion pathways

Constitutive: make and release; no signaling molecules vs. Regulated: concentrate and store; signaling for releasing (neural/endocrine)

Myoepithelial cell

Contraction of the myoepithelial cell compresses the acinus and helps in the expulsion of secretory products into the duct (secretory acinar pushes the saliva into the duct). AKA basket cell. Because of its contractile function, it requires actin. Actin can be identified using actinimmuno histology

Multicellular Exocrine gland development

Covering epithelia with subjacent connective tissue -proliferation and invasion Further differentiation -penetrate the underlying connective tissue -maintain or lose a connection with the surface epithelium Structure of multicellular exocrine glands: 1. simple gland = one unbranched duct -secretory portion may be tubular, coiled tubular, branched tubular, or acinar (flask-shaped) 2. compound gland = more than one duct that branches repeatedly -secretory portion may be tubular, acinar, or tubuloacinar *each secretory acini contains a secretory and conducting portion at the cellular level.

Two Types of Duct Cells

Duct cells not only serve as a duct to guide the saliva secretion, but they're also a part of the processing of primary saliva by modifying (electrolyte content)/condensing the primary saliva and secreting immunoglobin A. Intercalated duct cell = flat cuboidal Striated duct cell = low columnar

Gland secretion methods

Exocrine v. Endocrine (ductless) *The way the glands are developed determine whether its exocrine or endocrine. Difference between endocrine and exocrine is that the endocrine glands lose connection to the original epithelial tissue and become ductless; they do not have a duct that connects to the surface; secretions are thus delivered by the intertwining of blood vessels with the endocrine gland. Exocrine glands maintain their connections to the original epithelia and have a duct --> formation of secretory portion is made by secretory cells.

Gland defined

Formed by epithelial cells that secrete a fluid of different composition than blood or intercellular fluid--such as: ions, secretory polypeptides or proteins, lipids or glycoproteins.

Secretory granules

Secreted molecules are generally stored in the glandular epithelia in small membrane-bound vesicles; released upon certain stimuli

Glandular secretory cells

Serous producing cells = water secretions; usually intensely stained with eosin; nuclei usually rounded or oval. Merocrine secretion Glycoproteins are N-linked to the beta-amide of asparagine. vs. Mucous producing cells = viscous, slimy secretions; appear empty by routine H/E; nuclei often flattened against base of cell. Glycoproteins are O-linked to the hydroxyl groups of serine or threonine. *Note: the presence of empty cells helps differentiate between mucous and serous cells; also mucous cells are very flat; different linkage in glycoproteins.

Secreted substances of glands

proteins (pancreas) lipids (adrenal, sebaceous glands) complexes of carbohydrates and proteins (salivary glands) all three substances (mammary glands) Ion (sweat glands, low synthetic activity)